Final answer:
The transition from land-dwelling mammals with four limbs to modern whales with flippers is explained by natural selection, with evidence from ancestors like Pakicetus and Rodhocetus, and supported by genetic data indicating a common ancestor for diverse species.
The correct option is c.
Step-by-step explanation:
The change from four-limbed land animals to aquatic animals with two limbs functioning as flippers in the lineage that led to modern whales is best explained by natural selection.
As ancestral land-dwelling mammals ventured into aquatic environments, there was a selective pressure for adaptations that enhanced swimming abilities.
Over time, forelimbs evolved into flippers, which are an adaptive characteristic unique to aquatic environments, and hindlimbs receded, becoming vestigial structures in modern whales.
This transformation can be seen in fossil records of species like Pakicetus and Rodhocetus, which are considered ancestors of modern whales. Rodhocetus, for example, was a largely aquatic animal.
This evolutionary pathway highlights how mammals, including whales, dolphins, and porpoises, have adapted from land to a life in the ocean.
Genetic evidence supports that these modifications are a result of descent with modification from a common ancestor of whales, humans, and cats, despite varying skeletal structures.
The correct option is c.